One well-known type of heat exchanger is a plate heat exchanger. A plate heat exchanger is constructed using a series of plates in which each plate has two inlet holes, two outlet holes, and a series of channels. The channels allow a fluid to flow from one of the inlet holes to one of the outlet holes. The remaining inlet and outlet holes of each plate are sealed off from the channels by a gasket. By arranging several plates on top of one another in an alternating configuration, two intertwined fluid paths are created. Examples of such plates are depicted in FIGS. 1-3 of WIPO International Publication No. WO 93/01463, which is incorporated herein by reference in its entirety.
Rectangular heat exchanger plates are typically provided with a notch on each of the two short sides. The notch is shaped complementarily with a guide rail that guides the heat exchanger plates when they are stacked to form a plate heat exchanger. An assembled plate heat exchanger is therefore most unstable along the long sides, since they lack supporting guide rails.
Currently, to overcome this problem, the plate material outside the gasket groove of an individual heat exchanger plate is corrugated as shown in FIG. 3 of WO 93/01463 to give the plate edge relatively greater strength and flexural rigidity than plates formed with a plane protruding flange. This corrugation also gives greater stability when many heat exchanger plates are stacked and clamped together to form a plate heat exchanger.
The most common form of corrugation is to press the plate material into a trapezoidal shape so as to form a hive pattern when several plates are assembled to form a plate heat exchanger, but it is also known to use other forms of corrugation. Swedish Patent No. 165 960, incorporated herein by reference in its entirety, discloses a heat exchanger plate having a corrugation between the gasket groove and the edge of the heat exchanger plate, where the outer portion of the heat exchanger plate is shaped as a reinforcing band which is positioned at the underside of the pressed plate.
In spite of the advantages of such corrugation, it has been found that these types of heat exchanger plates continue to have some weaknesses. For example, the edges can collapse when subjected to extreme operating conditions. This causes the heat exchanger plates to tip over and the hive pattern to collapse, resulting in possible leakage of the exchange medium. This risk is particularly great if the heat exchanger plates are made of a thin plate material.